You could achieve some of this without an app at all: put iGoogle widgets for the features you desire on your iGoogle page, then keep a browser window open to that page in Safari in your iPad.

There are roughly a billion iGoogle widgets to choose from, and they include widgets for weather, calendars, news, Twitter, RSS, and more. You can choose the color theme too.

The main problems with this approach would seem to be that the display of information is not as compact on the screen as you could achieve with a custom-coded app, so it may be a problem to fit everything that you want so that you can see it all at once. Also, I haven't figured out a way to make the Google search bar go away, and it takes up an unfortunate amount of space at the top of the page (less so in the vertical orientation on an iPad, but more in the horizontal orientation).